Thermal Spray Research Articles

Breakthrough in atmospheric plasma spraying of high-density composite electrolytes: Deposition behavior and performance of plasma-sprayed GDC-LSGM on porous metal-supported solid oxide fuel cells

The potential application of plasma spraying in the preparation of ceramic electrolyte for porous metal-supported solid oxide fuel cells (SOFCs) is highlighted by its ability to eliminate the need for a high-temperature sintering process. However, the challenge of achieving highly dense electrolytes through plasma spraying remains to be addressed. In this study, a novel electrolyte for porous metal-supported SOFCs (PMS-SOFCs) is developed. This involved the preparation of a highly dense structure of gadolinium-doped ceria (GDC)-lanthanum strontium gallium magnesium oxide (LSGM) composite coating using plasma spraying under atmospheric conditions. The composite electrolyte is prepared using atmospheric plasma spraying (APS). The addition of the low-melting-point LSGM phase enhanced the microstructural densification of the GDC-based composite coating and diminished electron loss in a reducing atmosphere, thereby improving the cell's open-circuit voltage. At 36 kW plasma arc power, the single cell with composite electrolyte exhibited a maximum power density of 371 mw/cm2 at 750 °C and achieved the highest open-circuit voltage (1.03 V) at 600 °C. Moreover, the open-circuit voltage remained stable over a 100-h test. These findings suggest that using APS to deposit a composite electrolyte with added low-melting-point secondary phases presents a promising approach for achieving relatively high OCV in PMS-SOFCs based on cerium oxide electrolytes.

Pharmaceutical Quality by Design Approach to Develop High-Performance Nanoparticles for Magnetic Hyperthermia.

Magnetic hyperthermia holds significant therapeutic potential, yet its clinical adoption faces challenges. One obstacle is the large-scale synthesis of high-quality superparamagnetic iron oxide nanoparticles (SPIONs) required for inducing hyperthermia. Robust and scalable manufacturing would ensure control over the key quality attributes of SPIONs, and facilitate clinical translation and regulatory approval. Therefore, we implemented a risk-based pharmaceutical quality by design (QbD) approach for SPION production using flame spray pyrolysis (FSP), a scalable technique with excellent batch-to-batch consistency. A design of experiments method enabled precise size control during manufacturing. Subsequent modeling linked the SPION size (6-30 nm) and composition to intrinsic loss power (ILP), a measure of hyperthermia performance. FSP successfully fine-tuned the SPION composition with dopants (Zn, Mn, Mg), at various concentrations. Hyperthermia performance showed a strong nonlinear relationship with SPION size and composition. Moreover, the ILP demonstrated a stronger correlation to coercivity and remanence than to the saturation magnetization of SPIONs. The optimal operating space identified the midsized (15-18 nm) Mn0.25Fe2.75O4 as the most promising nanoparticle for hyperthermia. The production of these nanoparticles on a pilot scale showed the feasibility of large-scale manufacturing, and cytotoxicity investigations in multiple cell lines confirmed their biocompatibility. In vitro hyperthermia studies with Caco-2 cells revealed that Mn0.25Fe2.75O4 nanoparticles induced 80% greater cell death than undoped SPIONs. The systematic QbD approach developed here incorporates process robustness, scalability, and predictability, thus, supporting the clinical translation of high-performance SPIONs for magnetic hyperthermia.

Behavior of Bare, Cr3C2-20NiCr, and NiCrAlY coated Fe-Ni Based Superalloy Under Hot Corrosion in a 75 wt.% Na2SO4 + 25wt.% NaCl film at 9000C

The main aim of this research is to assess the resistance to hot corrosion of untreated Fe-Ni-based superalloys compared to those coated with Cr3C2-20NiCr and NiCrAlY. These superalloys are strengthened through precipitation with ɣ’ Ni3(Al, Ti) and further fortified using high-velocity oxy-fuel (HVOF) thermal spray coating. The evaluation is performed under harsh conditions consisting at a temperature of 900°C for a duration of 25 cycles in a mixture containing 75 wt.% Na2SO4 and 25 wt.% NaCl. An optical microscope (OM) is utilized to determine the coating thickness of the coated specimens. Corrosion kinetics are evaluated by measuring changes in mass at the conclusion of each cycle during the investigation of hot corrosion. Furthermore, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM) are employed to investigate the chemical composition, ascertain phases, and scrutinize the surface morphology of the corrosion products. The findings reveal that the Fe-Ni superalloy, coated with precipitation-strengthened layers, demonstrates enhanced resistance to hot corrosion compared to the uncoated substrates, as evidenced by reduced weight gain per unit area. The coated substrates are enveloped by protective oxide layers consisting of chromium, nickel, aluminum, and their respective spinels, effectively shielding the substrate surfaces. In contrast, The superalloy without coating, which underwent precipitation hardening within the substrate, showed instances of microspalling and sputtering of the oxide scale. Findings suggested that both Cr3C2-20NiCr and NiCrAlY coatings substantially improved resistance against hot corrosion. Noteworthy was the superior protective efficacy of the NiCrAlY coating over the Cr3C2-20NiCr layer, attributed to the development of protective oxide scales containing Cr2O3 and NiCr2O4.

Flame spray pyrolyzed carbon-encapsulated Au/Fe3O4 nanoaggregates enabled efficient photothermal therapy and magnetic hyperthermia of esophageal cancer cells.

Multifunctional magneto-plasmonic nanoparticles with magnetic hyperthermia and photothermal therapy could kill cancer cells efficiently. Herein, carbon-encapsulated Au/Fe3O4 (Au/Fe3O4@C) was fabricated using an enclosed flame spray pyrolysis. The nanostructures, including an Fe3O4 core (51.9-55.2nm) with a decreasing carbon shell thickness and an Au core (4.68-8.75nm) coated with 2-4 graphite layers, were tailored by tuning the C2H4 content in the reacting gas mixture. Saturation magnetization (33.7-48.2emu/g) and optical absorption were determined. The carbon shell facilitated the dispersion of Au/Fe3O4 and restrained their laser-induced and magnetic field-induced coalescence and growth. Au/Fe3O4@C exhibited excellent magnetic resonance imaging capability (91.4mM-1 s-1) and photothermal performance (65.4°C for 0.8mg/mL Au/Fe3O4@C at a power density of 1.0W/cm2 after 300s near-IR laser irradiation (808nm)). Moreover, the combined application of photothermal and magnetic-heating properties reduced the required intensity of both laser and magnetic field compared to the intensity of separate situations. Our work provides a unique, intriguing approach to preparing multicomponent core/shell nanoaggregates that are promising candidates for esophageal cancer cell therapy.

Oxidation and hot corrosion behavior of multicomponent coatings produced by atmospheric plasma spray

Oxidation and hot corrosion behavior of multicomponent coatings produced by atmospheric plasma spray

Strains and Stresses in Multilayered Materials Determined Using High-Energy X-ray Diffraction

This work explores the advantages and disadvantages of a methodology using high-energy X-ray diffraction to determine residual stresses in multilayer structures produced by atmospheric plasma spraying. These structures comprise a titanium alloy substrate (Ti64), a bonding layer (Ni-Al), and an abrasive coating (Al2O3). This study focuses on analyzing the residual stress gradients within these layers. The presented method is used to determine stresses across the entire thickness of multilayer structures. Experiments were carried out using a high-energy rectangular beam, operating in transmission mode, on the cross-section of the sample. The results indicate variable stresses throughout the depth of the sample, particularly near the layer interfaces. The semi-automatic methodology presented here enables us to follow stress evolution within the different layers, providing indications of the load transfer between them and at their interfaces. The sin2ψ method was used to analyze the diffraction data and to determine the stresses in each phase along the sample depth. However, interpreting results near the interfaces is complex due to the geometric and chemical effects. We present a discussion of the main advantages and disadvantages of the methodology for this kind of industrial sample.

Interfacial delamination mechanism of thermal barrier coatings with real microstructure considering gradient thermal and growth strains based on the fracture phase field

The interface of atmospheric plasma spray (APS) thermal barrier coatings (TBCs) is highly irregular and rough, while their microstructure is porous and extremely uneven. This complexity leads to intricate patterns during the growth of thermally grown oxide (TGO), the distribution and evolution of the generated stress, as well as the initiation and expansion of cracks. Along these lines, in this work, a phase-field theory considering both the thermal gradient strain and TGO growth was established to thoroughly investigate the interface oxidation cracking in TBCs. More specifically, a two-dimensional geometric model of APS TBCs was established, incorporating real interface morphology and microstructure. Numerical simulations and experiments were also conducted to study the temperature and stress distribution, as well as the underlying mechanism of interface cracking during the service of TBCs. The results indicated that at high temperatures, the bottom temperature of the top coating (TC) layer with a porosity of 3.1% and a thickness of 200 μm was approximately 5 °C lower than that of the TC layer without porosity. Compared to the ideal model without pores, the model considering the real microstructure, with the presence of microcracks in the TC, makes it easier for the normal stress in the TGO at the peak region to be released. The inter-lamella cracks (Type A) in the TC near the peaks initiated earliest, followed by the creation of inter-lamella cracks at other locations, accompanied by the appearance of lamella-fracture cracks (Type B), inter-lamella to interfacial cracks (Type C), inter-lamella to TGO cracks (Type D), and internal TGO cracks (Type E). The coalescence of all these types of cracks will ultimately lead to coating failure.

Thermal Spray Technology in Automotive Industry Applications

Thermal Spray Technology in Automotive Industry Applications

Effect of Thickness on the Residual Stress Profile of an Aluminum Cold Spray Coating by Finite Element Analysis

This research investigates the influence of thickness on residual stress profiles in aluminum cold spray coatings using finite element analysis (FEA). Residual stress is a critical factor that impacts coating adhesion, fatigue life, and susceptibility to delamination in thermal spray processes. Despite its acknowledged importance, predictive analysis of these stresses on a layer-by-layer basis remains relatively unexplored. This study introduces an innovative numerical methodology to analyze the progression of residual stresses across various deposition efficiencies (10%, 40%, 60%, and 100%) and layer thicknesses, thereby enhancing predictive accuracy for cold spray coatings. The findings demonstrate that the number of deposited layers significantly affects residual stress profiles in both coatings and the substrate, with compressive residual stress predominating in the coatings and deeper tensile stress predominating in the substrate. Residual stress behavior near the last deposited layer aligns with the expected peening effect. Discrepancies in substrate stress distributions may arise from variations in deposition parameters and unconsidered temperature effects. While the model generally aligns with theoretical and some empirical data, observed discrepancies underscore the need for further validation. This study lays the groundwork for informed decision-making for cold spray processes by providing insights into stress management, thereby contributing to enhancing coating integrity and performance.

High temperature infiltration behavior and reaction characteristics of Colima volcanic ashes on gadolinium zirconate coatings deposited by atmospheric plasma spraying

Volcanic ashes are considered a serious threat to the aircraft industry. At high temperatures, they inflict severe thermochemical damage to the typical 7 wt.% yttria-stabilized zirconia thermal barrier coatings that protect the aircraft turbine. There is a need to evaluate alternative materials with excellent resistance to infiltration of molten siliceous particles, such as gadolinium zirconate. In this work, free-standing thermal barrier coatings of gadolinium zirconate were manufactured by atmospheric plasma spraying, varying deposit parameters to obtain different relative densities to evaluate the infiltration of molten Colima volcanic ashes for 1 h and 10 h at 1250 °C. The infiltration depth and the reaction products resulting from each interaction, were studied by different characterization techniques. In general, the coatings show high resistance to the infiltration of the volcanic ashes, reaching infiltration depths between 50 µm and 80 µm after 10 h of infiltration time. In this sense, gadolinium zirconate coatings are excellent candidates against the infiltration of Colima volcanic ashes compared to the typical yttria-stabilized zirconia-based thermal barrier coatings.

Numerical analysis of thermal spray coatings using artificial neural networks (ANN) overview

Numerical analysis of thermal spray coatings using artificial neural networks (ANN) overview

Investigating the properties of sprayed insulating cementitious materials with corn cobs

As the mining depth increases, the underground space will face more serious thermal hazards. By using corn cobs, an agricultural waste, to prepare cementitious insulation materials, active insulation layers are constructed by injecting insulation materials into underground spaces using cementitious material spraying techniques. This article designed the ratios of corn cob sprayed cementitious materials and analyzed the changes in the properties of the materials obtained by adding 0–25% of corn cobs. The results of the study showed that the addition of different proportions of corn cobs improved the thermal insulation properties of the material by 6.9%-75.5% as compared to the ordinary mortar material. The mechanical properties became 25.9%-113.6% of the original. When the corn cob is wetted for more than 10 min, the fluidity of the material is sufficient to reach the minimum standard for spraying operations. Considering the comprehensive performance of the material, it is concluded that the wetting time of 30 min, the addition of corn cob 20%, the corn cob particle size of 200 mesh, and the amount of sand doping of 40% are the optimal ratios of the studied corn cob spraying cementitious materials. The study of corn cob lightweight thermal insulation spray cementitious material is of great significance for controlling the ambient temperature in deep underground space, promoting cleaner production and improving the use of environmental resources.

Study on the corrosion performance of supersonic atmospheric plasma sprayed Cr3C2-NiCr coatings

PurposeDue to the harsh underground environment in coal mining, the surface of hydraulic support columns corrodes severely, resulting in significant economic losses. Therefore, a highly corrosion-resistant coatings is needed to extend the service life of the columns.Design/methodology/approachThis study aims to compare the corrosion resistance of ST-Cr3C2-NiCr (sealed treatment Cr3C2-NiCr) coatings with industrially applied chromium plating. The corrosion failure mechanism of the coatings was investigated.FindingsThe results demonstrated that the ST-Cr3C2-NiCr coatings exhibited excellent corrosion resistance. After sealing treatment, the corrosion potential of Cr3C2-NiCr coatings was −0.215 V, and the corrosion current density of Cr3C2-NiCr coatings was lower than that of the plated parts.Practical implicationsST-Cr3C2-NiCr coatings prepared by supersonic atmospheric plasma spraying could provide excellent corrosion resistance in the coal industry.Originality/valueThe low porosity and the presence of the NiCr phase were crucial factors contributing to the preferable corrosion resistance exhibited by the ST-Cr3C2-NiCr coatings. The corrosive process of the coatings involved layer-by-layer delamination of surface oxide film, sub-surface pitting, formation and degradation of sub-surface passive film, as well as severe block-like delamination.

Effects of Al2O3 content on the microstructure and performance of Inconel 625-xAl2O3 composite non-skid coatings by plasma enhanced high-velocity arc spraying

The efficient preparation of metal/ceramic composite coatings with excellent performance has been a hot research topic in the field of thermal spraying. In this study, a novel plasma enhanced high-velocity arc spraying (PE-HAS) technique is developed. A series of Inconel 625-xAl2O3 composite non-skid coatings are deposited by PE-HAS with different feeding ratio of alloy wire (1.6 mm in diameter) and ceramic powder (13.5 μm in average particle size). Specifically, the microstructure, mechanical properties, corrosion resistance and tribological performances of the coatings have been comprehensively investigated. Results indicate that all of the composite coatings with different Al2O3 contents are characterized by high densities, low defects (porosity≤3.52 %), strong bonding (≥50 MPa) and high friction coefficient (≤ 1.034). The coatings with low Al2O3 content feature a more homogeneous structure and superior bonding strength. The microhardness and wear resistance of the coatings increases significantly with increasing Al2O3 content, which should be attributed to the formation of many localised enhancement areas composed of different forms of Al2O3 phases. It is worth noting that the unique feedstock feeding method promotes the formation of the in-situ double-layer structure of coatings with high Al2O3 content, which further improves the wear and corrosion resistance. However, the friction coefficient gradually decreases when the Al2O3 content is too high, thus affecting the anti-slip performance of the coating.

Prediction of HVAF thermal spraying parameters and coating properties based on improved WOA-ANN method

In this study, high-velocity air fuel (HVAF) thermal spray technology was utilized to deposit Hastelloy C276 powder onto 316 L stainless steel substrates. The effects of various spray process parameters such as propane pressure, air pressure, spray distance, and powder feeding rate on the microstructure, microhardness, and corrosion resistance of the coatings were investigated. In addition, the coupling effects among multiple spray parameters were considered by employing a combined approach with the Improved Whale Optimization Algorithm (IWOA) and Artificial Neural Network (ANN) model, and the mapping relationships between the spray process parameters and coating porosity, microhardness, and corrosion current density was established. The results revealed that the prepared C276 coating exhibits lower porosity, higher microhardness, and exceptional corrosion resistance. And the IWOA-ANN model outperforms the ANN model and WOA-ANN model in the prediction accuracy and stability for all three performance measures, particularly for porosity and microhardness. Furthermore, the comparison between experimental results and predicted results validates the reliability and accuracy of the trained IWOA-ANN model, demonstrating its efficacy in predicting HVAF spray parameters and coating properties.

Tribological performance of functional coated fiber reinforced additively manufactured polymer composite

Additive manufacturing has witnessed an upward trend in utilization across diverse industries in recent years. This study examines the tribological properties of polymer composites produced using additive manufacturing. The polymer composites were produced using the fusion deposition modeling process. Subsequently, they undergo thermal spray coating and spin coating processes that deposit hafnium carbide particles onto their surface. The wear test studies were conducted at three distinct temperature levels in accordance with the ASTM standard procedure. The findings demonstrated that the application of a ceramic particle coating led to a substantial decrease in the specific wear rates. Additionally, there were observed differences in the wear rates depending on the specific methods used for applying the coating. The application of thermal coating shown high efficacy in reducing wear rates and safeguarding the underlying materials against material loss. The uncoated carbon fiber reinforced polylactic acid (PLA-CF) material showed a slightly significant amount of material degradation as the test chamber temperature increased, in comparison to the coated specimens. The average specific wear rate of the thermally coated carbon fiber reinforced polylactic acid specimen at a temperature of 70 °C is 0.000156 kg Nm−1.

Improvement of heat resistance in silicone rubber by Fe-doped TiO2 nanoparticles prepared via flame spray pyrolysis

In recent years, the development of heat-resistant silicone rubber has been a research hotspot. In this paper, a kind of Fe doped TiO2 nanoparticles (Fe-TiO2) was prepared via flame spray pyrolysis, which can significantly improve the high temperature resistance of silicone rubber. The results show that, on the one hand, the prepared Fe-TiO2 can inhibit the breakage of Si-O main chain; on the other hand, because Fe is doped into the lattice of TiO2, it causes the change of TiO2 crystal phase and produces more oxygen vacancies, which is more beneficial to capture free radicals in silicone rubber matrix, so that Fe-TiO2 can effectively inhibit the excessive cross-linking of silicone chain caused by methyl oxidation on the side of silicone rubber. TGA results showed that after adding Fe-TiO2, the 5 % thermal weight loss temperature of methyl vinyl silicone rubber increased from 392.8 °C to 435.6 °C.

Performance of Atmospheric Plasma-Sprayed Thermal Barrier Coatings on Additively Manufactured Super Alloy Substrates

This work represents a preliminary study of atmospheric plasma-sprayed (APS) Yttria-Stabilized Zirconia (YSZ)-based thermal barrier coatings (TBCs) deposited on forged and additive manufactured (AM) HAYNES®282® (H282) superalloy substrates. The effect of different feedstock morphologies and spray gun designs with radial and axial injection on APS-deposited YSZ layer characteristics such as microstructure, porosity content, roughness, etc., has been investigated. The performance of TBCs in terms of thermal cycling fatigue (TCF) lifetime and erosion behaviour were also comprehensively investigated. In view of the high surface roughness of as-built AM surfaces compared to forged substrates, two different types of NiCoCrAlY bond coats were examined: one involved high-velocity air fuel (HVAF) spraying of a finer powder, and the other involved APS deposition of a coarser feedstock. Despite the process and feedstock differences, the above two routes yielded comparable bond coat surface roughness on both types of substrates. Variation in porosity level in the APS topcoat was observed when deposited using different YSZ feedstock powders employing axial or radial injection. However, the resultant TBCs on AM-derived substrates were observed to possess similar microstructures and functional properties as TBCs deposited on reference (forged) substrates for any given YSZ deposition process and feedstock.

Feasibility research of perovskite‐type PrAlO3+δ as high‐temperature infrared radiation coating

AbstractThermal radiation coating with low thermal conductivity and high infrared emissivity are desirable. In this work, a novel rare‐earth aluminate (PrAlO3+δ with rhombohedral structure) was synthesized via solid‐state reaction method, and the corresponding coating was fabricated using atmospheric plasma spraying (APS). The study encompassed an investigation into the phase structure, high‐temperature phase stability, thermo‐mechanical characteristics, and infrared properties. The results illustrate that as‐deposited coating contained amorphous phase, but recrystallized coating presented phase stability up to 1600°C. Furthermore, the recrystallized coating exhibited low thermal conductivity of 1.35 W/m K at 900°C as well as an average coefficient of thermal expansion of 10.36 × 10−6/K. Also, the coating exhibited high infrared emissivity related to high valance state (Pr4+) and oxygen vacancies. And the average infrared emissivity within 2–14 µm was 0.822 at 1300°C and presented slight decrease with the increase of temperature (the average infrared emissivity of 0.795 at 1800°C).

Highly bioactive hydroxyapatite coating made by flame spray technique

This research involves fabrication and characterization of flame sprayed hydroxyapatite (HA) coatings on 316 stainless steel substrates where the desirable structure with high porosity can be obtained. Nano-sized HA powder was synthesized and calcined at 600 °C. The subsequent powder was used as feedstock powder for flame spray technique (FS). In-flight particles of HA were spherical with the range of particle size between 3–37 µm. The average coating thickness was 128 µm and the crystalline phases were a mixture of HA and tricalcium phosphate (TCP). Simulated body fluid (SBF) test showed that HA layer was formed after 7 days. Highly bioactive properties were due to high surface area from rough coating and porous structure, which would be beneficial from the flame spray technique. The coating is promising for applications in biomedical field.